Re: text conventions/spec. round off &c

Subject: Re: text conventions/spec. round off &c
From: "L. H. Garlinghouse" <garlinghou -at- WATERLOOINDUSTRIES -dot- COM>
Date: Mon, 13 Apr 1998 14:20:27 -0600

Helen Cygnarowicz queries:

> > can i please have your reactions to this statement:
> >
> > centimeters is not an accepted international unit of measure. it
> > should be either meters or millimeters.
> >
> > can i also have your thoughts on this:
> >
> > it is not necessary to list a dimension to five significant digits,
> > e.g., 210.98 mm wide. this number should be rounded up to 211 mm.
> >
> > it was my impression that in a Specification list, the exact
> > dimensions
> > should be used, but in a text reference, rounding up is ok. am i off
> > the
> > mark here?
RE: cm v. mm. There should be a style book or a drafting
room manual that should clear this up. If not, I refer to
"Machinery's Handbook (19th edition) page 2347, "Metric
Dimensions on Drawings." It says: "The length units of the
metric system that are most generally used in connection with
any work relating to mechanical engineering are the meter
and the milimeter. On mechanical drawings, all dimensions
are generally given in millimeters, no matter how large the
dimensions may be. In fact, dimensions of such machines as
locomotives and large electrical apparatus are given
exclusively in millimeters. This practice is adopted to
avoid mistakes due to misplacing decimal points." It goes on
to say that in some cases decimal points can be dropped
completely as 1 mm is less than 0.040."

Although my reference is from 1971, I suspect that the above is still
reasonable. Note although that it focuses on mechanical drawings. I
think I recall seeing civil engineering drawings with callouts in
cm somewhere in a past life, however.

I submit that engineering drawings are but one form of technical
communications and that there is/should be some overlap of style
convention between narrative documents and drawn documents.

As to the cm being "legal," I don't know. The liter is not
recognized but an awful lot of beverages are still being sold in
liters. Again, there should be a drafting room manual or some style
book that give direction in your particular application.

RE: Rounding specs in text. My reaction (being a Quality wonk in
manufacturing) was one of fear an trepidation.

Example: In the early ISO driven documentation efforts at a
manufacturing plant, documentation was written that duplicated the
specifications on the engineering drawing. This was defensible as
management chose to make engineering drawings unavailable to the
manufacturing people (!!). Thus the text documents was the only
means of communication of the spec, short of word of mouth, and
notes on the back of an envelope or on Post-its.

As time progressed, (and management became enlightened) drawings and
other source documents WERE made available to manufacturing people.
This allowed referring to nominal dimensions in the narrative text.
This was defensible as the instructions required that the engineering
drawing be referred to as the source for actual sizes and tolerances.

If the purpose of the text is to communicate dimensions, they should
(IMHO) be in exactly the same format and level of precision as on the
source engineering document. Mfg. folks have been burnt too many
times to not take things literally. A dimension of 1.5" is NOT
going to be seen by a manufacturing person as interchangeable with
one written as 1.50" or 1.500" as each one is going to be seen as
having its own tolerance.

I may have missed some subtlety in this whole thread and gone off on
a tangent. If so, perhaps it was still entertaining and perhaps

<< All opinions, statements, &c are my own>>
L.H. Garlinghouse, C.Q.E.
Pocahontas AR U.S.A.
(870) 892-4586 ext 7659
garlinghou -at- waterlooindustries -dot- com

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